Polymeric materials used for a variety of applications may be divided into "fully reacted" systems and "reactive" systems. Fully reacted systems are those materials which are synthesized by the supplier and are delivered in finished fashion to the molder or the user. Examples of fully reacted systems include polyethylene, polypropylene and nylon. Reactive systems are delivered in semi-finished or monomeric form by the supplier to the molder or the user and undergo further reaction. Examples of reactive systems include polyurethanes (which are the reaction product of isocyanates and polyols), polyureas (which are the reaction product of isocyanates and amines or water), epoxies, reactive acrylics, alkyds and many others.
These multi-component nonaqueous reactive systems are used extensively to produce polymeric coating compositions (e.g. paints), adhesives, sealants, and the like. Because the individual components react with each other, it has been difficult to formulate nonaqueous reactive component combinations which have the necessary performance properties, have the reactive capability needed to form the finished product, yet have a long shelf life under normal storage conditions. Useful reactants are chosen on the basis of many factors and the generally recognized problem is that there are multiple constraints placed on the "ideal" reaction component combination. It is important to provide nonaqueous reactive component combinations that do not sacrifice one property (e.g., long shelf life) in order to satisfy another property (e.g., reactive capability or end-use properties).
In order to overcome these difficulties, it is common to utilize reactant systems in which the reactants are stored in separate formulations or are compartmentalized in such a manner that the reactants are combined with one another just prior to use or application. In one type of nonaqueous reactive chemistry, an adhesive mixture is applied to the surfaces to be joined and then either reacts spontaneously, or has the reaction rate enhanced through heat, absence of oxygen, catalysts or other means. In another example, commonly used equipment known in the art to formulate polyurethane coatings utilizes two high energy component streams, i.e. a polyol and an isocyanate, that are mixed before application. In a typical paint spray application line (see U.S. Pat. No.4,999,213), a stream of polyol and a stream of isocyanate are mixed in an in-line mixer just before application. Under ideal conditions, this mixed stream flows promptly and cleanly through the paint spray application equipment before any reaction occurs between the polyol and the isocyanate. However, any stoppage of application of the paint, as often occurs, or a breakdown of the equipment, results in the formation of soft and hard particles in the application equipment.
Other methods have been devised to compartmentalize the reactants in order to increase the shelf life and decrease the contact time between the reactants prior to actual commingling. One method is to use less reactive pre-polymers or capped reactants such as capped isocyanate groups.
Encapsulation of reactants (e.g., isocyanate) is also used and processes are well known for producing capsules of reactive materials, exemplified by U.S. Pat. No. 3,409,461. It is known that highly reactive solids and reactive liquids may be compartmentalized by encapsulation through a variety of chemical and physical means including, but not limited to, interfacial polymerization in a liquid medium, in-situ polymerization, two component nozzle polymerization, centrifugal polymerization, spray drying, fluid bed drying and rotational suspension separation encapsulation. Nevertheless, prior art encapsulation methods may require additional steps in preparing the reactants and impingement mixing of two or more reactants requiring elaborate equipment, may require high temperatures to release the encapsulated materials, may introduce undesirable foreign materials into the product as the residue of encapsulant and may only be suitable for certain types of reactants, such as solids. Gels have unique properties that may offer significant advantages as compartments for reactive chemicals but, to our knowledge, encapsulation of gels containing reactive chemicals has not been successfully accomplished.
Therefore, the generic problem of maintaining the integrity of several highly nonaqueous reactive components in a reaction mixture is still problematic. The specific problem of forming polymer articles such as polyurethanes and the like under controlled conditions and at reasonable rates still has not been satisfactory resolved.